The wireless local-area network (WLAN) technology known as “Wi-Fi” has been standardized by IEEE in the 802.11 series of specifications (i.e., as “IEEE Standard for Information technology—Telecommunications and information exchange between systems. Local and metropolitan area networks—Specific requirements. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”).
The IEEE 802.11 specifications regulate the functions and operations of the Wi-Fi access points (APs) or wireless terminals, collectively known as “stations” or “STA,” in the IEEE 802.11, including the physical layer protocols, Medium Access Control (MAC) layer protocols, and other aspects needed to secure compatibility and inter-operability between access points and portable terminals. Wi-Fi is commonly used as wireless extensions to fixed broadband access, e.g., in domestic environments and in so-called hotspots, like airports, train stations and restaurants.
Recently, Wi-Fi has been subject to increased interest from cellular network operators, who are studying the possibility of using Wi-Fi for purposes beyond its conventional role as an extension to fixed broadband access. These operators are responding to the ever-increasing market demands for wireless bandwidth, and are interested in using Wi-Fi technology as an extension of, or alternative to, cellular radio access network technologies (RATs). Network operators that are currently serving mobile users with, for example, any of the technologies standardized by the 3rd-Generation Partnership Project (3GPP), including the radio-access technologies known as Long-Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS)/Wideband Code-Division Multiple Access (WCDMA), and Global System for Mobile Communications (GSM), see Wi-Fi as a wireless technology that can provide good additional support for users in their regular cellular networks.
In particular, cellular network operators are seeking ways to offload traffic from their cellular networks to Wi-Fi, e.g. in peak-traffic-hours and in situations when the cellular network for one reason or another needs to be off-loaded, e.g. to provide requested quality of service, maximise bandwidth or simply for coverage.
Portable wireless devices or terminal devices (also referred to in 3GPP as user equipments—UEs) today usually support both Wi-Fi and a number of 3GPP cellular technologies, but many of the terminal devices are effectively behaving as two separate devices from a radio access perspective. The 3GPP radio access network (RAN) and the modems and protocols that are operating pursuant to the 3GPP specifications are basically unaware of the wireless access Wi-Fi protocols and modems that are operating pursuant to the 802.11 specifications.
Techniques for access network selection (i.e. the selection of which type of network, e.g. 3GPP or WLAN, a UE should access or connect to) and traffic steering (i.e. the selection of a network to be used for a particular data flow) are being discussed and agreed in 3GPP. In Release-12, LTE/WLAN interworking has been standardized so that among others the eNB can provide the UE with “RAN rules”, i.e. thresholds, which the UE evaluates and based on that steers traffic between LTE and WLAN. The thresholds values could be, for example, for metrics such as 3GPP signal-related metrics Reference Signal Received Power (RSRP)/Reference Signal Received Quality (RSRQ)/Received Signal Code Power (RSCP)/EcNo, WLAN signal-related metrics such as Received Channel Power Indicator (RCPI)/Received Signal Strength Indicator (RSSI), WLAN load/utilization, WLAN backhaul load/capacity, etc. Furthermore, it is decided in the mobility management entity (MME) which traffic is off-loadable/steerable, e.g. voice-over-Internet protocol (VOIP) traffic may stay in LTE while other traffic is off-loadable. This happens on packet data network (PDN) connection level. Additionally, in Release 13 it is envisaged that the UE provides the eNB with WLAN measurements, that the eNB can consider when providing the UE with RAN rules. Furthermore, it is discussed that the eNB can provide the UE with a dedicated traffic steering command to move traffic between LTE and WLAN.
Another way in which cellular network operators intend to use Wi-Fi is to use aggregation. 3GPP/WLAN aggregation is a feature whereby a UE may at least receive (and possibly also transmit) data using links to both the 3GPP network and a WLAN. This is similar in principle to dual connectivity within LTE, but it aggregates carriers from different radio access technologies (RATs), e.g. a 3GPP network and Wi-Fi. 3GPP/WLAN aggregation is currently being standardized by 3GPP in Release 13 as part of “LTE-WLAN Radio Level Integration and Interworking Enhancement”, RP-150510 which was submitted to 3GPP TSG RAN Meeting #67 in Shanghai, China on 9-12 Mar. 2015.
In a split bearer architecture option for LTE/WLAN aggregation in the downlink, data is split on a packet data convergence protocol (PDCP) layer in the eNB (which is a term used to describe a radio base station in LTE). The eNB may route PDCP packet data units (PDUs) dynamically via eNB radio link control (RLC) to the UE directly, or via a backhaul channel to WLAN and then to the UE. In a separate bearer architecture option, the lower layers of a bearer are switched to LTE or WLAN meaning all PDCP packets of that bearer are routed via either LTE or the WLAN side.
FIG. 1 shows an exemplary protocol architecture for LTE/WLAN aggregation and illustrates a protocol architecture for the eNB 2, a “WLAN termination point” 4 and a UE 6. Other protocol architectures are also being considered. The WLAN termination point 4 in the network is denoted WLAN termination (WT) and may be implemented by a WLAN access point (AP) and/or access controller (AC) or another network node. The interface protocol between eNB 2 and WT 4 is denoted Xw and is used to exchange control plane and user plane information between the eNB 2 and WT 4.
For mobility, it is envisaged that the eNB or other network node in the 3GPP network is in control of which WLANs a UE should consider for access network selection, traffic steering and/or traffic aggregation. However, the UE is in control of which node is actually used for aggregation and/or which network is selected for access and which network node traffic is steered to. Thus, an eNB or other network node can provide the UE with a set of WLANs or WLAN nodes that the UE can consider when deciding which node to use for aggregation, access network selection or traffic steering. In some cases the decision on where the UE steers traffic to, which particular network is accessed or which node is used for aggregation may be transparent to the eNB. This set, or a similar set, may also be used when performing access network selection or traffic steering. The set may be provided in the form of a set of identifiers for the WLANs or WLAN nodes, which may be Service Set Identifiers (SSIDs), Extended SSIDs (ESSIDs), Homogeneous ESSIDs (HESSIDs), Basic SSIDs (BSSIDs), or a realm identifier. This set is referred to herein as a mobility list or a mobility set.